fix(validation): drop the orphaned medication clock-skew constant

The shared validateEntryInstant guard now owns the future clock-skew
allowance, so the medication-local TAKEN_AT_CLOCK_SKEW_MS export is dead.
Remove it; medication intake keeps its tighter 5-year floor via
TAKEN_AT_MAX_AGE_MS. Clears the dead-code gate.

src/lib/validations/medication.ts

@@ -204,7 +204,6 @@ function hhmmToMinutes(hhmm: string): number {
  * validator's window. Slot-distance / medication-start checks stay in
  * the routes — the schema cannot see the medication.
  */
-export const TAKEN_AT_CLOCK_SKEW_MS = 5 * 60 * 1000;
 export const TAKEN_AT_MAX_AGE_MS = 5 * 365 * 24 * 60 * 60 * 1000;
 
 /**